Antenna reflectors



Jan. 19, 1960 E. w. BALL ANTENNA REFLECTORS 2 Sheets-Sheet l Filed Nov. 17, 1954 A TTORNEV Jan. 19, 1960 E. w. BALL 2,922,161

ANTENNA REFLECTORS Filed Nov. 17. 1954 2 Sheets-Sheet 2 /NVENTOR ELDON W BA L1.

,4 TTORNEV ANTENNA REFLECTORS Eldon W. Ball, Melrose, Mass, assignor to Raytheon Company, a corporation of Delaware Application November 17, 1954, Serial No. 469,463

Claims. (Cl. 343-912) This invention relates to an antenna reflector and to a method of fabricating the same.

The reflecting surface of antennas, particularly those adapted for use at microwave frequencies, must be very accurately constructed in order to obtain a suitable radiation pattern. In the past, it has been customary to achieve the required degree of accuracy of reflector shape by machining the reflector surface. Machining of large antenna reflector surfaces, however, is relatively difficult and laborious, especially if complex curvatures are required. If a slat-type reflector is used instead of a solid reflector, the surface to be machined can be reduced, but the reflector may well be deformed substantially during the machining process.

In accordance with the subject invention, an antenna reflector of sturdy construction and having a reflecting surface of high accuracy is achieved without maintaining close tolerances on the reflector during assembly. The reflector face comprises a group of elongated channels through which several spaced reflector elements are inserted; the reflector face is clamped to an accurate form or mold of the desired configuration. Each of the channels is partially filled with cement.

The reflector supporting structure includes members disposed parallel to the elongated channels of the reflector face and these members contain flanges or ribs projecting toward said reflector face. The framework is positioned so that the ribs of the framework members extend into the fluidal cement contained within corresponding aligned channels of the reflector face. The supporting framework is maintained in this position until the cement has hardened sufficiently to provide a rigid jointure of the reflector face and reflector supporting framework. After the cement has been cured, the complete antenna reflector assembly, which includes a highly accurate reflector face bonded to a rigid supporting structure, is then withdrawn from the mold by removing the mold clamps. Once an accurate mold has been obtained, any number of accurate antenna reflectors may be obtained readily and economically without maintaining any close tolerances other than on the manufacturing mold.

The novel features of the invention will best be understood from the following description when read in connection with the accompanying drawings in which:

Fig. 1 is a perspective view illustrating the manner of shaping an antenna reflector face over a mold of the desired shape;

Fig. 2 is a front view of a complete antenna reflector assembly in accordance with the invention;

Fig. 3 is a plan view of the antenna reflector assembly of Fig. 2; and I Fig. 4 is a detail view illustrating the manner of joining the reflector face to the reflector supporting structure.

In Fig. 1 of the drawing, there is illustrated a portion of a mold or form 10, whose surface configuration conforms to that of the reflecting surface of the antenna reflector to be constructed. Mold 10 may be made of woodor any rigidmetal or plastic which is readily sus- Patented Jan. 19, 1960 ceptible of machining and which is sufficiently resistant to deformation. The surface 11 of mold 10 contains a plurality of spaced slots 12 for receiving corresponding elongated channels 13. Each channel contains apertures 14 adjacent the web or base portion 15; these apertures are equally spaced along the length of the channel. A multiplicity of reflector elements 16 in the form of rods or wires are threaded through the various apertured channels, as clearly shown in Fig. 1. It will be noted that the spacing between adjacent apertures in the'various channels 13 is made equal to the desired spacing between reflector rods 16. These rods are spaced apart, not only to provide a lighter antenna construction, but also to reduce wind resistance to a minimum. The spacing between rods will, of course, depend upon the electrical operating characteristics desired. The size and configuration of the reflector elements may differ from that shown in the drawing so long as a sufliciently large reflecting surface is available for reflecting energy impinging thereon. For example, reflecting elements 16 may be in the form of either broadside or edgewise strips, in which case, the apertures in channels 13 would be rectangular rather than circular. I

The depth of the slots '12 in mold surface 11 is such that reflector rods 16 contact the mold throughout the length of the mold. In other words, the depth of slots 12 is substantially equal to the distance between the bottom edge of apertures 14 in channels 13 and the bottom .of the channel web 15.

The several rods 16 are clamped down tightly against mold surface 11 by means of clamping bars 17 which are attached securely to the mold at points about midway between the channels by means of screws 18, or some other-fastening devices. In order to facilitate mounting and clamping of the reflector rods on the mold, the rods are rolled to nearly the correct radius prior to threading them through the channels. A fluidal cement 19 is poured into the channel for purposes which will be ex: plained subsequently.

In Figs. 2 and 3, a supporting structure 20 is shown, which consists of a plurality of mechanically interconnected stringers 21, crisscross braces 22, and upright frame members 23. The component parts of supporting structure 20 are preferably made of aluminum tubing in order to achieve a minimum weight consistent with mechanical strength. Supporting structure 20, however, may be made of any rigid material and may be of any desired shape. Each frame member 23, which is affixed at the ends, as by welding, to upper and lower stringers 21, consists of a generally tubular portion 24 and a stem or rib 25 extending radially from the tubular portion as shown in Figs. 2 to 4.

The particular supporting structure 20, shown in Figs. 2 and 3, is but one of the many possible rigid mechanical z frameworks; the details of the framework will depend upon the weight of the reflector face to be supported, wind and corrosion resistance requirements, availability of stock, and other mechanical design factors. The only limitation on the supporting structure 20 is that the' front edges 26 of upright frame members 23 should be arranged along a curve which reasonably approximates the curvature of the desired antenna reflector surface.

Supporting structure 20 is lowered toward mold 10 until the ribs 25 of frame members 23 are in proximity with the corresponding channels 13 aflixed to the mold. The diameter of the apertures 14 in channels 13 are slightly larger than that of the reflector rods 16, thereby permitting the channels to be moved in a direction parallel to the longitudinal axis of the rods. The position of its corresponding channel 13.

siderable latitude in alignment, the width of each slot 12 is considerably greater than that of the channel. When all the ribs of frame members 23 are aligned with the openings in corresponding channels 13, the latter are filled to about one-half their depth with the fluidal cement '19, already preferred to, which'has a high degree of aflinity for metal and high mechanical strength in compression, tension, and shear.

Epoxy resins with 100% solids content have proven very satisfactory, as cements and bonds with aluminum may be obtained, capable'of withstanding stresses up to 4500 pounds per square inchwell above that of most refractory or rubber cements. The epoxy cements contain no solvents or other materials which evaporate during hardening, and consequently, there is no shrinkage at the cemented joints. The viscosity of the fluidal cement preferably is increased by the addition of inert matter, such as glass fibers, which do not react chemically with the cement but which do prevent the latter from flowing out of the channels onto the reflector rods during assembly, thereby altering the electrical characteristics of the antenna. Other types of thermosetting resins, such as phenolics, may be used in lieu of the epoxy cements provided they are free of water or other solvents which cause shrinkage during the curing process.

After necessary adjustment of the channels has been accomplished, the corresponding ribs of the supporting structure are lowered into the cement-filled channels until every one of the ribs has penetrated the cement sulficiently for adequate bonding between channels 13 and supporting structure 20. The depth of the channels is such that ample contact of cement andmetal is achieved even with a generous tolerance on the shape of the supporting structure. The weight of the supporting structure, as the ribs of the frame members are lowered into the'channels, will normally cause complete self-alignment of the channels and the frame members of the supporting structure. The strength-to-weight ratio of the supporting structure, however, should be such that no distortion of the reflector face occurs in assembly. In some cases, pressure may be applied to the supporting structure during assembly to the reflector face. As shown in Fig. 4, some of the cement is forced into the region between rods 16 and channels :13, as well as in the region between channels 13 and the ribs 25 of the frame members 23.

The thermosetting cement is then cured for a period of time necessary to effect polymerization and then cooled gradually to ambient temperature until the cement becomes solid. In order to facilitate hardening of the cement, a hardening agent, such as an amine hardener, is added to the cement; the hardener produces an exothermic reaction which in some cases provides sufiicient heat to cure the resinous cement. For example, the cement will cure in about twenty-four hours when exposed to ambient temperatures. If the cement is heated to a temperature at which polymerization occurs, the cement will harden more rapidly; this temperature varies, depending upon the type of cement used. Once the cement is completely cured, the cement firmly unites the rod and channels of the reflector face, as well as bonding the reflector face to the supporting structure.

As heretofore mentioned, one of the features of this invention is that the antenna supporting framework need not be accurately shaped, since the depth of the channels is sufiicient to permit adequate bonding in spite of varying degrees of penetration of the ribs of the frame mem bers into the cement-filled channels. If tolerances are maintained sufiiciently close on the supporting structure, however, the channels may be clamped to the surface of the mold, instead of being adjustably mounted within slots. In this case, the reflector rods would be spaced slightly above the mold surface instead of flush with said surface. In either case, strips of paper which are imperyious to liquids may be inserted beneath the channels to prevent excess cement from bonding the channels and the rods to the mold. If, however, a cement of proper viscosity is used and adequate care taken, these protective strips may be eliminated.

This invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in the art. For example, this invention is not limited to the cements heretofore described, since any cementitious material may be used which provides a sufliciently strong bond between the reflector face and the supporting structure. Furthermore, any supporting structure may be used which provides adequate mechanical support for the reflector face, in accordance with well known techniques of structural design. it is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. A method of fabricating an antenna reflector of a given desired configuration comprising the steps of clamping a reflector face assembly consisting of a series of elongated reflector elements located within spaced channels to a mold whose surface configuration conforms to the aforesaid desired configuration, at least partially filling each of said channels with a fluidal cement, positioning portions of a supporting structure into said channels, and bonding together said supporting structure and said reflector face assembly with a cementitious material.

2. A method of fabricating an antenna reflector of a given desired configuration comprising the steps of clamping a reflector face assembly consisting of a series of elongated reflector elements located within spaced channels to a mold whose surface configuration conforms to the aforesaid desired configuration, at least partially filling each of said channels with a fluidal cement, positioning portions of a supporting structure into said cement-filled channels, and curing said cement until it attains a solid state.

3. A method of fabricating an antenna reflector of a given desired configuration comprising the steps of clamping a reflector face assembly consisting of a series of elongated reflector elements located within spaced channels to a mold whose surface configuration conforms to the aforesaid desired configuration, at least partially filling each of said channels with a viscid fluidal cement, positioning portions of a supporting structure into said cement-filled channels, curing said cement until it attains a solid state and unclamping said reflector elements from said mold.

4. A method of fabricating an antenna reflector of a given desired configuration comprising the steps of inserting a plurality of reflector elements through spaced apertured channels, connecting said elements to a mold having a surface whose configuration conforms to the aforesaid desired configuration, positioning portions of a supporting structure into said channels, and bonding said supporting structure to said channels and said reflector elements.

5. A method of fabricating an antenna reflector of a given desired configuration comprising the steps of inserting a plurality of reflector elements through spaced apertured channels, clamping said elements to a mold slotted to receive said channels and having a surface whose configuration conforms to the aforesaid desired configuration, placing a fluidal cement into said channels, positioning portions of a supporting structure into said cement-filled channels, and curing said cement until it attains'a solid state.

6. A'method of fabricating an antenna reflector of a given desired configuration comprising the steps of inserting a plurality of reflector elements through spaced apertured channels, clamping said elements to a mold slotted to receive said channels and having a surface whose configuration conforms to the aforesaid desired configuration, placing a fluidal cement into said channels, positioning portions of a supporting structure into said cement-filled channels, curing said cement until it attains a solid state, and unclamping said elements from said mold.

7. An antenna reflector comprising a plurality of parallelly disposed channels conta'ming apertures spaced along the length thereof, a multiplicity of elongated reflecting elements extending through said apertured channels substantially perpendicular thereto, a supporting structure including members each having an elongated rib portion extending into a corresponding one of said channels, and a cementitious binding material located within said channels for fixedly joining said supporting structure to said channels.

8. An antenna reflector comprising a reflector face :assembly and a supporting structure, said reflector face assembly including a plurality of parallelly disposed channels containing apertures spaced along the length thereof and a multiplicity of elongated reflecting elements disposed substantially perpendicular to said channels, said apertures being of greater diameter than the diameter of said reflecting elements, said supporting structure including members each having a portion extending into a corresponding channel, and a binding material located within said channels and Within the region between said channels and said elements for fixedly joining said supporting structure to said reflector face assembly and for fixedly joining said elements to corresponding channels.

9. An antenna reflector comprising a reflector face assembly and a supporting structure, said reflector face assembly including a plurality of parallelly disposed channels containing apertures spaced along the length thereof and a multiplicity of elongated reflecting elements extending through said apertured channels substantially perpendicular thereto, said supporting structure including members each having an elongated rib portion extending into a corresponding one of said channels, and a binding material located within said channels and Within the region between said channels and said elements for fixedly joining said supporting structure to said reflector face assembly and for fixedly joining said elements to corresponding channels.

10. An antenna reflector comprising a reflector face assembly and a supporting structure, said reflector face assembly including a plurality of spaced parallel channels containing apertures spaced along the length thereof, a multiplicity of elongated reflecting elements extending through said apertured channels, said supporting structure including members each having an elongated rib portion extending into a corresponding one of said channels, and a binding material located within said channels for fixedly joining said supporting structure to said channels, said supporting structure being disposed entirely on the back side of said reflector face assembly.

References Cited in the file of this patent UNITED STATES PATENTS 1,316,088 Eagan Sept. 16, 1919 2,049,070 Mathieu July 28, 1936 2,255,184 Osenberg Sept. 9, 1941 2,270,314 Kraus Jan. 20, 1942 2,540,518 Gluyas Feb. 6, 1951 2,703,842 Lewis Mar. 8, 1955 OTHER REFERENCES The Iron Age, August 19, 1943, pp. 5253. 

